Prior to the present invention, various methods were employed to synthesize bisphenols, such as bisphenol-A, by effecting reaction between a ketone and a phenol. One procedure, for example, involved the use of large amounts of inorganic acid catalysts, such as sulfuric acid or hydrochloric acid. Experience has shown, however, that the use of inorganic acids requires a means to neutralize such acids at the end of the reaction due to the corrosive action of the strong acids. In addition, distillation of the resulting bisphenol is often required because of the many by-products formed during the reaction under high acid conditions.
An improved procedure was developed to synthesize bisphenols by using a solid resin cation-exchange catalyst to effect phenol-ketone condensation. A disadvantage of the ion-exchange catalyst, however, is its relatively low acid concentration resulting in slow reaction rates. Rate acceleration has been achieved through the use of mercaptans. Apel et al. U.S. Pat. No. 3,153,001, shows incorporation of mercaptan by partial esterification of the ion-exchange catalyst in the form of a sulfonated insoluble polystyrene resin. Another procedure (McNutt et al, U.S. Pat. No. 3,394,089) shows the partial neutralization of aromatic sulfonic acid with alkylmercaptoamine. A further procedure is shown by Wagner et al. U.S. Pat. No. 3,172,916, based on the partial reduction of the sulfonic acid to afford thiophenol functional groups.
Further improvements in synthesizing bisphenols from ion-exchange resins are shown by Faler et al. U.S. Pat. Nos. 4,294,995, 4,346,247, and 4,396,728, assigned to the same assignee as the present invention and incorporated herein by reference. Faler et al. utilize certain N-organoaminodisulfide to incorporate covalently bonded organomercaptan groups into the backbone of sulfonated aromatic organic polymer.
Although particular improvements have been obtained by using ion-exchange resins of the prior art, it has been found that available ion-exchange resins comprising sulfonated aromatic organic polymer having chemically combined aminoorganomercaptan groups do not provide a satisfactory degree of activity, selectivity and stability with respect to catalyzing the conversion of a ketone to a bisphenol as a result of reaction with a phenol.
As utilized hereinafter, the expression "catalyst activity", or "% conversion" (% C) means ##EQU1## Catalyst activity is calculated under continuous steady-state reaction conditions from data obtained at a temperature of 60.degree. C. to 85.degree. C. In measuring catalyst activity, ion-exchange resin is used having an attachment level of about 4 to 40 mole percent of aminoorganomercaptan sites, at a Weight--Hour--Space--Velocity (WHSV) averaging about 3.0 to 16.0 parts of feed, per part of ion-exchange resin, per hour.
The expression "selectivity", or "S", is specific to the production of bisphenol-A and is calculated as follows: ##EQU2## The selectivity value is also calculated from data obtained under continuous steady state and WHSV conditions as defined above.
The term "stability" with respect to defining the characteristics of ion-exchange resins having chemically combined aminoorganomercaptan groups means the ability to resist change in % conversion and selectivity under continuous steady-state operating conditions as previously defined. In calculating ion-exchange resin stability, an initial average "base" value for % conversion and selectivity is determined over a period of up to 4 days under continuous steady-state conditions. A subsequent average "trial" value for % conversion and selectivity is thereafter computed by continuous use of the ion-exchange resin for a period of up to 60 days. Catalyst stability is expressed as follows as a % conversion variance "% CV" over the trial period: ##EQU3##
The present invention is based on the discovery that substantial improvements in conversion of acetone to bisphenol, and higher yields of p-p-bisphenol-A can be obtained by using effective amounts of sulfonated aromatic organic polymer having from about 4 to 40 mole percent of ionically bound aminoorganomercaptan groups of the formula, ##STR1## where R is a C.sub.(3-10) divalent organo radical, and R.sup.1 is a C.sub.(3-8) monovalent alkyl radical.
For example, it was found that sulfonated cross-linked polystyrene resin having about 24 mole percent of ionically bound n-propylaminopropylmercaptan groups within the scope of formula (1) provided a 69% conversion of acetone and had a selectivity of 45.8 during an initial 4 days continuous run which fell to only a 68.8% conversion and a selectivity of 44.8 after 25 to 28 days of continuous operation. This was found to be substantially superior to sulfonated cross-linked polystyrene resin having about 21 mole percent of ionically bound aminoethylmercaptan groups which showed under the same continuous reaction conditions for making bisphenol-A, a 57.0% conversion and a selectivity of only 27 which was substantially maintained over a 25-28 day period. On the other hand, a sulfonated cross-linked polystyrene resin having about 18 mole percent of covalently bound propylaminopropylmercaptan groups, had a % conversion of 71.9 and a selectivity of 35.2 after the four day base period which fell to a % conversion of less than 40 and a selectivity of less than 24 after a 25-28 day trial run.